The present invention relates to cardiac assist devices, and in particular to a magnetohydrodynamic (MHD) heart pump which is less intrusive, and more effective, and easier to implement than prior art designs. The system of the present invention has no moving parts to wear out or break down, and is far less invasive than prior art systems.
The preferred embodiment of the present invention contemplates a cardio assist device utilizing MHD, wherein first and second, parallel electrodes forming an electrode assembly are placed, via the patient""s femoral artery, into the aorta in the vicinity of the abdomen, which electrode assembly is exposed to a high density magnetic field generated outside of the patient. A current generated by a control unit energizes the first and second electrodes, and the blood situated therebetween, causing the high density magnetic field to interact with the energized blood, hydrodynamically motivating said blood to flow through the electrode assembly, in a uniform direction, thereby providing a fluid pumping force and pressure commensurate with the product of the magnetic field strength and the induced current in the blood vessel in accordance with MHD theory and practice, the general operational theory of which was first understood and explained by Scottish physicist James C. Maxwell in the mid-19th century.
In the preferred embodiment of the invention, the magnetic field is generated exterior of the patient via a superconducting magnet which is designed to produce a large magnetic field in the middle torso of the patient, so that the electrode assembly is generally centrally disposed within the magnetic field, along a longitudinal axis aligned with the aorta (and/or vena cava), and with electrode current flow generally orthogonal to the magnetic field.
Sensors monitoring the patient may utilize electrocardiogram (ECG), blood pressure, and blood flow, and other data to control the current in the blood in order to vary the pumping pressure and flow, so as to emulate the pumping action and intensity of the patients heart in real time, so as to lessen the trauma of artificial pumping assistance, or bypass on the patient.
The present device may also be utilized to provide full cardiac blood flow, as when a heart is stopped for bypass surgery, or to provide targeted limb or organ perfusion in a patient.
Nearly one million acute cardiac failure fatalities occur each year in the U.S., many of which would have been preventable if there had been developed a suitable artificial heart. Heart assist or left ventricular assist devices (LVADs) are currently large, very invasive (requiring major chest surgery) and represent a significant patient risk.
These pumps require surgery to implant tubes, wires and other large devices to provide the motive pumping power which normally enters and exits the body cavity in the chest area. Typically large and percutaneous devices, they represent a significant surgical risk in their implementation, even if they do provide the necessary coronary assistance. Removing these devices requires another major bout of surgery with the attendant risks.
Another problem with current LVAD devices is the possibility that the quality of circulation provided by the units, which lack the sophistication of being able to emulate the natural rhythm of the heart, are that they may provide insufficient blood flow to the brain or other organs, to the extent that serious medical consequences arise. Finally, most of the LVAD pumps currently in use cause some destruction of red blood cells due to the destructive mechanical pumping means utilized.
A plethora of artificial heart designs have been contemplated and tested, including:
Cardio-pulmonary bypass machines, which are utilized in bypass surgery when the heart is stopped and the pumping action is taken over by a machine exterior from the patient that uses a mechanical pumping action such as a roller pump. These machines are for temporary use only, and require extensive thoracic invasion and medication for implementation and use. Long term use would be fatal, and even short term use can result in hemorrhaging, infection, renal failure, stroke, and other serious effects.
An Archimedes type screw device was available for some time that was inserted in the femoral artery and advanced into the Aorta as a type of mechanical LVAD. It would spin fast and propel blood along the length of the Aorta toward the feet.
An intra-aortic balloon pump (IAPB) has been around for about 20 years. It is inserted in the Aorta blown up partially obstructing the aorta when the heart pumps. This helps preserve the heart and brain blood flow in times of low cardiac output by lowering the afterload on the heart and increasing flow to the coronary arteries and carotid arteries.
Artificial hearts are generally mechanically similar to the mechanical LVADs, but are configured to replace the entire heart (both the left and right side). These devices have been implemented both internally and externally, but with likewise unsatisfactory results.
All of the above devices are very invasive, requiring massive and lengthy thoracic surgery . The support equipment for these pump designs generally require chest penetrations and significant cardiac trauma for installation, sometimes including penetration of the heart itself. Lastly, the mechanical pumping action in all of the above designs is believed to cause damage to the blood constituents.
A list of patents which may have some pertinence to the present invention include:
U.S. Pat. No. 4,838,850 teaches an Electromedical Treatment Apparatus and which contemplates utilizing MHD effect to urge blood flow through blood vessels to increase circulation in targeted areas of the body. This patent does not contemplate the insertion of a device within the vasculature, but rather contemplates the use of magnetic lens to facilitate concentrated magnetic fields at a target area within the body, which may include a blood vessel, to utilize MHD effect to urge circulation of blood therethrough. (Col 7, lines 5-32).
U.S. Pat. No. 2,612,109 contemplates an earlier MHD pump design from the 50""s.
U.S. Pat. No. 5,888,241 teaches a cannula pump driven by an impeller to assist the ventricals of the heart. The device comprises a tube which includes magnetic windings for driving the impeller.
See also 5,851,174.
U.S. Pat. No. 5,911,685 teaches an Intravascular micro axial pump which may be installed by advancing same through the patients vasculature, avoiding invasive chest surgery. The system incorporates an electrically driven, micro-motor having an impeller for pumping.
U.S. Pat. No. 5,385,581 teaches a Magnetically Suspended and Rotated Rotor in the form of a blood pump. This patent contemplates providing an impeller suspended and driven by a magnetic field, and includes feedback means in the form of sensors to monitor the patient, and computer control means to energize the coils with currents having frequency and amplitude adjusted in relation to the blood pressure at the pump inlet, so as to match the flow characteristics of the pump to physiological characteristics of the natural heart. Further, U.S. Pat. No. 5,928,131 also teaches a magnetically suspended, impeller driven heart pump with control means configured to simulate the beating of the patient""s natural heart. See also U.S. Pat. Nos. 5,685,700 and 5,470,208, other magnetically suspended impeller systems configured to form blood pumps or the like.
U.S. Pat. No. 5,762,599 entitled xe2x80x9cMagnetically-Coupled Implantable Medical Devicesxe2x80x9d teaches a variety of implantable devices, including pumps, valves, a bone stretching device, and an artificial sphincter which are driven by external drive magnets mounted for rotation externally about the subjects body, thus incorporating teachings of relevance to the present, searched for invention, although nonetheless distinguishable therefrom.
U.S. Pat. No. 5,891,134 teaches what may be considered to be the use of MHD technology to provide heat to tissue.
U.S. Pat. No. 5,763,951 teaches an MHD pump for a circuit board developed by Northrop Grumman.
U.S. Pat. No. 5,668,420 teaches an MHD propulsion system design for ships, submarines or the like utilizing a superconducting solenoid coil within a tube having a helical flow path, the system utilizing a coil configured to provide about 6-12 Tesla, and is provided as an example of this application, of which several patents have issued.
U.S. Pat. No. 4,265,680 issued 1981 teaches a Method of Making Hollow Magnetic Pipe for conveying conductive fluid in magnetohydrodynamic energy amplification systems; U.S. Pat. No. 4,252,605 also teaches a tube which may have MHD applications.
In summary, the prior art has contemplated blood pumps, artificial hearts, LVADs and the like relying upon mechanical pumping mechanisms which have included, for example, impellers, helical screws, bladders, pistons, vacuum, centrifugal, peristaltic pumps and the like. The above systems have considerable documented shortcomings including:
pumps incorporating an impeller design or the like tend to damage blood cells;
mechanical pumps have a limited life span which is not assured due to premature failure;
infection can be a problem, not only with the sterility of the unit itself, but also with the drive means, which often is exterior to the patient (ex. fluid driven heart pump);
the pumping action (hydrostatic pressures) can facilitate circulatory and red blood cell damage, renal failure, strokes, and a long list of other damaging effects;
the pumping action has limited capabilities for control and feedback, and generally cannot be satisfactorily varied to imitate the natural rhythm and flow of the heart; and
internal pumps require massive invasion into the chest of the patient, and may require the complete severing and splicing a major artery to the unit.
Thus, there exits the need for a cardiac assist device which is minimally invasive and quickly implemented, providing a circulatory flow which is effective for life support, while being non-damaging to the patient.
The present invention utilizes magnetohydrodynamic technologies which have been proven for use in submarines and ships as propulsion systems, wherein first and second electrodes are employed along opposing walls of a conduit to provide a current flow through seawater situated therebetween. A superconducting, high field strength magnet is then employed to provide a high (known to be as high as 20 Tesla) magnetic field line of flux orthogonal to the current flow, which causes hydrodynamic forces upon the electrified seawater in accordance with Maxwell""s equations, thereby pumping the seawater through the system with no moving parts or vibrations.
The present invention contemplates an adoption of this technology in a wholly new and different field, i.e., to provide an MHD cardiac assist device which is safe and effective to use, requiring minimal invasive surgery for implementation on a rapid basis, while providing a circulatory flow which is effective for life support.
Cardiovascular disease accounts for nearly 1 million deaths each year in the U.S. For many coronary patients, the heart could repair much of its own damaged muscle if part of the pumping effort were temporarily taken over by some assist device. If this assist device could be placed into and removed from the patient by way of their femoral blood vessels, for instance, the patient""s heart blood flow could be maintained, as required, while reducing the physical load on the heart and allowing the injured muscle time to recover. This recovery period is expected to be from a few days to a few weeks, at which time the assist device would be turned off and removed from the patient.
The major advantage of the present invention, as compared to existing LVAD designs, is that the surgery risks to the already traumatized heart do not need to be taken. Rather, the present invention, an MHD-based LVAD uses the well established and relatively non-invasive catheter technology to install electrodes within a major blood vessel of the patient, well away from the heart, in order to facilitate blood flow. The present invention is designed for rapid, nominally invasive deployment, providing the urgent assistance needed by an acute cardiac failure patient, unlike the current support devices.
Installation of the system of the present invention could be performed in an emergency room, which frequently is where the temporary pumping assistance is often needed. The only additional equipment needed would be a high field magnet (not unlike current MRI magnets), and the special catheters and associated electronics to power the pump through small wires within the catheter structure.
In the present invention, the blood vessel pressure waveform can be modified specifically to avoid the problem of starving a specific organ due to reduced blood flow, by appropriate programming of the electronics that drive the pump, thus modifying the pressure during specific times of the periodic pumping cycle. Finally, most of the LVAD pumps currently in use cause some destruction of red blood cells. In contrast, the MHD pump of the present invention has no moving parts which should avoid the mechanical destruction of the blood components.
Existing LVAD devices require a large amount of electrical or pneumatic energy. Supplying this energy through percutaneous terminals or through an A.C. energy source and the attendant transformer through the skin coupling devices are the only alternatives available. Neither one of these alternatives is free from the risks of surgery and later infections, and supporting the mass of this equipment within the body cavity is a significant task.
By contrast, the pumping action of the MHD LVAD pump of the present invention is the result from the interaction of a high strength magnetic field generated by a magnet external to the patient, and a low level current conducted across the internal diameter of a blood vessel via a length of electrode. The electronics which drive the present pump would be external to the subject, and intrinsic electrical signals from the subjects heart used to synchronize the pumping signals utilizing cardiac signal sensors or commonly inserted ECG electrodes. Finally, the external magnetic field can be selected so that the current density in the blood stream is low enough to avoid excessive joule heating.
Heart assist devices should be designed to assist the heart while it repairs itself by taking over part of the hearts mechanical pumping work. The current technology of placing devices and tubes into and around the heart itself produces more traumatized heart muscle that must then be repaired by the hearts own resources in addition to the effort required to repair the damage that caused the initial need for emergency treatment.
In contrast, the present inventions technique of placing and removing the pumping device by the way of a major blood vessel using catheter technology eliminates trauma to the heart and the surrounding structure. If further surgery is required on the heart itself, the cardiac surgeon has a site with no scar tissue problems resulting from previous cardiac support device surgery.
Most heart patients, when the problem is the pump mechanism itself, are brought to a treatment center (hospital emergency room) and need immediate assistance or they will die. The use of drugs is of limited benefit, and an external heart/lung machine takes a lot of time to setup to take over the pumping task. The installation and implementation of a conventional LVAD requires major surgery as well as the use of a heart/lung machine during part of the operation. For an LVAD to be of maximum use in saving the life of a person with this class of heart trauma, the device must be implanted and started very quickly. Ideally, this should be accomplished in the emergency room itself, or in a nearby Intensive Care Unit containing the necessary equipment.
It is this unmet need for an immediate pumping aid, to allow time for the heart to repair itself, that the present invention provides, as indicated, without the need for invasive and risky thoracic surgery.
That the MHD pump of the present invention will pump a conductive liquid in the presence of a properly oriented magnetic field is beyond question, the technology already proven and successfully demonstrated, as discussed above, for an advanced submarine propulsion concept. Further, the drive technologies employed in the present invention is based upon a fundamental theory of magnetism developed by James C. Maxwell, namely, that a conductor containing a transverse magnetic field and an electrical current flowing orthogonal to this field will have a force applied upon the conductor which is proportional to the product of the current times the magnetic field strength. It is this fundamental principle which will allow the present invention to effectively and safely, without mechanical movement, hydrodynamically pump blood utilizing a simple electrode assembly situated within the blood vessel, in conjunction with a high field strength magnet which may be readily made utilizing presently available materials and technologies.
In addition to use as an LVAD, the system of the present invention may also be utilized to enhance limb perfusion in a variety of circulation disorders, including, for example, blood clots, thrombosis, frostbite, limb re-attachment, organ perfusion, carotid perfusion in cases of carotid artery spasm after angiogram, and increased profusion for acute stroke syndrome.
Another major intended use for this device is a by-pass pump support for coronary artery by-pass surgery. While electrodes in the abdominal aorta will provide a magnetohydrodynamic motive force away from the heart, one similarly placed in the Inferior vena cava of the abdomen with the electrodes oriented opposite the aortic ones will in turn pump blood toward the heart. With both electrodes energized and independently controllable, complete cardiac pumping action may be taken over for the heart just as it is currently done with a heart by-pass machine, but with major improvement.
Namely, with the present system, a profound advantage is created that gives surgeons the ability to perform lifesaving by-pass surgery without the need to grossly open the chest cavity. Current cardiac by-pass apparatuses require the chest cavity be opened to install large tubes into the heart and major blood vessels so that the blood can be removed from the body and circulated through a pumping machine. After external by-pass is established, then the heart can be stopped to allow repair of coronary blood vessels.
In contrast, in the MHD system of the present invention, the chest opening is not necessary to establish artificial circulation. The pump electrodes will be inserted through a blood vessel (s) such as the femoral artery and vein then the electrodes will be advanced into the aorta and inferior vena cava respectively. Electrode polarity will be such that the aorta has flow away from the heart and the inferior vena cava has flow toward the heart.
This push-pull action of the MHD pump will allow full blood flow at rest. Once this is in effect, much less invasive procedures can occur to repair coronary blood vessels such as through an endoscope. Through an endoscope the heart may be stopped electrically as is commonly done with open procedures, then coronary artery by-pass surgery procedures may be preformed. The heart would be restarted through an endoscope and the scopes removed.
By not opening the chest, patient""s would not have to suffer through the risk, pain, and other problems associated with the current method of by-pass surgery such as: having their sternum cut in half, ribs stretched and broken, massive bleeding, life threatening scar tissue build up on the heart and internal chest cavity, blood pumped outside the body for support, lengthy invasive surgery, massive exposure of the internal chest to infection to just mention a few.
Therefore, it is anticipated that the present invention and system will reduce morbidity and mortality greatly from surgery such as a CABG (coronary artery bypass grafting) for the above reasons. One could make a similar comparison to medical improvement with the laproscopic way of performing gallbladder surgery verses the previous way of removing the gallbladder through a large incision in the abdominal wall. The older, what was termed xe2x80x9copenxe2x80x9d, surgery would expose patients to a higher level of infection, more bleeding, pain, complications, longer procedure, and much longer recovery time. The xe2x80x9copenxe2x80x9d procedure would bring with it a six to eight week recovery time while with a laproscopic procedure a weekend of recovery is all that is necessary. In this case, as with a CABG, getting to the location to do the procedure is much worse than the procedure itself.
It is therefore an object of the present invention to provide a minimally invasive cardio pump which is quickly installed and effective in operation.
It is another object of the present invention to provide a cardio pump which has no moving parts and which pumps blood in such a fashion as to lessen the chances of damage to same.
It is another object of the present invention to provide a cardio pump which provides a pumping action which is based upon real time data from the heart of the patient, in order to optimize flow.
It is another object of the present invention to provide a cardio pump system wherein the electrodes are relatively inexpensive to manufacture and which may be disposable so as to provide maximum sterility.
Lastly, it is an object of the present invention to provide a method and system for cardiac heart assist utilizing magnetohydrodynamic drive utilizing a magnet exterior of the patient to generate a high density magnetic field about a portion of the torso of a patient, and a length of electrode placed within a major blood vessel of the patient within the magnetic field, in order to provide MHD flow of blood or other conductive fluid in the vicinity of the electrode, to support the heart of the patient.